diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f13f9c1..2b8c09c 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -460,6 +460,25 @@ typedef union WALInsertLockPadded
 } WALInsertLockPadded;
 
 /*
+ * State of an exclusive backup
+ *
+ * EXCLUSIVE_BACKUP_NONE means that there is no exclusive backup actually
+ * running, to be more precise pg_start_backup() is not being executed for
+ * an exclusive backup and there is exclusive backup in progress.
+ * EXCLUSIVE_BACKUP_STARTING means that pg_start_backup() is running and
+ * that is is not done yet.
+ * EXCLUSIVE_BACKUP_IN_PROGRESS means that pg_start_backup() has finished
+ * running and an exclusive backup is in progress. pg_stop_backup() is
+ * needed to finish it.
+ */
+typedef enum ExclusiveBackupState
+{
+	EXCLUSIVE_BACKUP_NONE = 0,
+	EXCLUSIVE_BACKUP_STARTING,
+	EXCLUSIVE_BACKUP_IN_PROGRESS
+} ExclusiveBackupState;
+
+/*
  * Shared state data for WAL insertion.
  */
 typedef struct XLogCtlInsert
@@ -500,13 +519,14 @@ typedef struct XLogCtlInsert
 	bool		fullPageWrites;
 
 	/*
-	 * exclusiveBackup is true if a backup started with pg_start_backup() is
-	 * in progress, and nonExclusiveBackups is a counter indicating the number
+	 * exclusiveBackupState is changed to EXCLUSIVE_BACKUP_STARTING for the
+	 * duration of pg_start_backup(), then to EXCLUSIVE_BACKUP_IN_PROGRESS once
+	 * it is done, and nonExclusiveBackups is a counter indicating the number
 	 * of streaming base backups currently in progress. forcePageWrites is set
 	 * to true when either of these is non-zero. lastBackupStart is the latest
 	 * checkpoint redo location used as a starting point for an online backup.
 	 */
-	bool		exclusiveBackup;
+	ExclusiveBackupState exclusiveBackupState;
 	int			nonExclusiveBackups;
 	XLogRecPtr	lastBackupStart;
 
@@ -9833,7 +9853,7 @@ do_pg_start_backup(const char *backupidstr, bool fast, TimeLineID *starttli_p,
 	WALInsertLockAcquireExclusive();
 	if (exclusive)
 	{
-		if (XLogCtl->Insert.exclusiveBackup)
+		if (XLogCtl->Insert.exclusiveBackupState != EXCLUSIVE_BACKUP_NONE)
 		{
 			WALInsertLockRelease();
 			ereport(ERROR,
@@ -9841,7 +9861,7 @@ do_pg_start_backup(const char *backupidstr, bool fast, TimeLineID *starttli_p,
 					 errmsg("a backup is already in progress"),
 					 errhint("Run pg_stop_backup() and try again.")));
 		}
-		XLogCtl->Insert.exclusiveBackup = true;
+		XLogCtl->Insert.exclusiveBackupState = EXCLUSIVE_BACKUP_STARTING;
 	}
 	else
 		XLogCtl->Insert.nonExclusiveBackups++;
@@ -10096,7 +10116,7 @@ do_pg_start_backup(const char *backupidstr, bool fast, TimeLineID *starttli_p,
 		{
 			/*
 			 * Check for existing backup label --- implies a backup is already
-			 * running.  (XXX given that we checked exclusiveBackup above,
+			 * running.  (XXX given that we checked exclusiveBackupState above,
 			 * maybe it would be OK to just unlink any such label file?)
 			 */
 			if (stat(BACKUP_LABEL_FILE, &stat_buf) != 0)
@@ -10178,6 +10198,16 @@ do_pg_start_backup(const char *backupidstr, bool fast, TimeLineID *starttli_p,
 	PG_END_ENSURE_ERROR_CLEANUP(pg_start_backup_callback, (Datum) BoolGetDatum(exclusive));
 
 	/*
+	 * Mark that start phase has correctly finished for an exclusive backup.
+	 */
+	if (exclusive)
+	{
+		WALInsertLockAcquireExclusive();
+		XLogCtl->Insert.exclusiveBackupState = EXCLUSIVE_BACKUP_IN_PROGRESS;
+		WALInsertLockRelease();
+	}
+
+	/*
 	 * We're done.  As a convenience, return the starting WAL location.
 	 */
 	if (starttli_p)
@@ -10195,8 +10225,8 @@ pg_start_backup_callback(int code, Datum arg)
 	WALInsertLockAcquireExclusive();
 	if (exclusive)
 	{
-		Assert(XLogCtl->Insert.exclusiveBackup);
-		XLogCtl->Insert.exclusiveBackup = false;
+		Assert(XLogCtl->Insert.exclusiveBackupState == EXCLUSIVE_BACKUP_STARTING);
+		XLogCtl->Insert.exclusiveBackupState = EXCLUSIVE_BACKUP_NONE;
 	}
 	else
 	{
@@ -10204,7 +10234,7 @@ pg_start_backup_callback(int code, Datum arg)
 		XLogCtl->Insert.nonExclusiveBackups--;
 	}
 
-	if (!XLogCtl->Insert.exclusiveBackup &&
+	if (XLogCtl->Insert.exclusiveBackupState == EXCLUSIVE_BACKUP_NONE &&
 		XLogCtl->Insert.nonExclusiveBackups == 0)
 	{
 		XLogCtl->Insert.forcePageWrites = false;
@@ -10280,14 +10310,21 @@ do_pg_stop_backup(char *labelfile, bool waitforarchive, TimeLineID *stoptli_p)
 	WALInsertLockAcquireExclusive();
 	if (exclusive)
 	{
-		if (!XLogCtl->Insert.exclusiveBackup)
+		if (XLogCtl->Insert.exclusiveBackupState == EXCLUSIVE_BACKUP_NONE)
 		{
 			WALInsertLockRelease();
 			ereport(ERROR,
 					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 					 errmsg("exclusive backup not in progress")));
 		}
-		XLogCtl->Insert.exclusiveBackup = false;
+		if (XLogCtl->Insert.exclusiveBackupState == EXCLUSIVE_BACKUP_STARTING)
+		{
+			WALInsertLockRelease();
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("exclusive backup currently starting")));
+		}
+		XLogCtl->Insert.exclusiveBackupState = EXCLUSIVE_BACKUP_NONE;
 	}
 	else
 	{
@@ -10301,7 +10338,7 @@ do_pg_stop_backup(char *labelfile, bool waitforarchive, TimeLineID *stoptli_p)
 		XLogCtl->Insert.nonExclusiveBackups--;
 	}
 
-	if (!XLogCtl->Insert.exclusiveBackup &&
+	if (XLogCtl->Insert.exclusiveBackupState == EXCLUSIVE_BACKUP_NONE &&
 		XLogCtl->Insert.nonExclusiveBackups == 0)
 	{
 		XLogCtl->Insert.forcePageWrites = false;
@@ -10597,7 +10634,7 @@ do_pg_abort_backup(void)
 	Assert(XLogCtl->Insert.nonExclusiveBackups > 0);
 	XLogCtl->Insert.nonExclusiveBackups--;
 
-	if (!XLogCtl->Insert.exclusiveBackup &&
+	if (XLogCtl->Insert.exclusiveBackupState == EXCLUSIVE_BACKUP_NONE &&
 		XLogCtl->Insert.nonExclusiveBackups == 0)
 	{
 		XLogCtl->Insert.forcePageWrites = false;